In developing a termination system of the type described in the cross-referenced application, a need developed to detect alarms relating to a loss of power in a plug-in unit. Because of the plug-ins limited number of input/output pins, power and cost considerations, previously used methods were not a good choice. For example, previously used methods included using a supervisory resister which would draw a current in the event of an open circuit downstream thereof. The prior art of a current source to a resistor cannot identify which unit fails. A similar technique will be used on the line side of a fuse in a printed circuit board to detect an open therein or some other open circuit condition.